Machine tools having large rotary members, such as swinging arm robots, are constructed so as to attenuate or reduce detrimental effects of reaction forces generated when the rotary members are moved. Typically, a servo motor or the like is mounted to a base of the machine, with the rotary member moved by the motor or via a gear or pulley arrangement. When the rotary member is moved, reaction forces of the motor are absorbed into the heavy, well dampened mass of the base, which is generally of rigid cast iron or polymer machine construction and may be further secured to a concrete floor or other heavy foundation to further dampen these reaction forces.
While generally effective, the mass needed to provide dampening for these reaction forces is expensive, as is the structure needed to support the mass of the machines. Further, machine accuracy is limited by the mass of the machine base and its rigidity due to the fact that reaction forces are attenuated and not eliminated. Further yet, with increasing machining speeds, flexure of the base occurs when heavy loads are applied thereto by the motor, in turn causing machine accuracy to deteriorate proportionally.
The principles governing behavior of rotating bodies, hereinafter denoted as gyroscopic masses, are well understood, and have been used for many years in many forms as sensor elements to provide stabilizing signals for control of various vehicular contrivances, particularly aircraft. In other applications, relatively large gyroscopic masses, known as Control Moment Gyroscopes, (CMG) have been developed and mounted in spacecraft and used to maintain a fixed attitude of the spacecraft through the use of gyroscopic forces. From the 1970s through the present, HONEYWELL CORP (TM) of Phoenix, Ariz. has been a major source of CMG technology as well as reaction wheel systems for satellite attitude control. During this time, extensive efforts have been made to refine performance capabilities and reliability of CMG technology. Among these endeavors was the successful development of a magnetically suspended reaction wheel for the Annular Momentum Control Device.
While the use of gyroscopic masses for stabilization purposes is well known, Applicant is unaware of any effort to use a gyroscopic mass to affect rotary movement of machine tools. Here, advantages are believed to be numerous, and include elimination of flexure of the mount of a machine tool by powering a rotary member mounted thereto without the power source being coupled to the mount. As such, the mount does not receive any reaction forces from the power source during rotation of the rotary member, but serves merely as a pivot for rotation. As a result, the base and supporting structure for the rotating member may be constructed using less weight and less attendant costs. Also, machining accuracy should increase due to greater closed loop positional control of the rotating member. Further, it is believed that undesirable vibrations that typically cause "chatter" during a machining operation are dampened or otherwise reduced by the gyroscopic mass.
A primary feature of the invention is the fact that ability to produce torque on a rotating member using a gyroscopic mass is dependent on two variables, namely rate of gimbal movement and momentum of the gyroscopic mass. For larger momentum values, small gimbal rates produce significant precession torques, which may be used to move the rotating member through large excursions or apply greater force to a metalworking tool during a metalworking operation. These small gimbal rates may be achieved using linear actuators such as solenoids, hydraulic cylinders or by rotary motors. Another advantage is that since the rotating member typically rotates in a horizontal plane, and the linear actuators produces gimbal motion against the rotating member in a vertical plane, no cross-coupling of these forces occurs. As a result, reaction forces of the linear actuators against the rotating member do not act as a disturbance input in the control arm scheme. Yet another advantage of the present invention is that the gyroscopic mass, when undisturbed, maintains a fixed orientation of the rotatable member without applying reaction forces to the mount or base of the machine. This is superior to conventional servo systems, which when held stationary apply reaction forces to the base, causing a loss of machining accuracy.
In the parent application to this case, now U.S. Pat. No. 5,655,412, a system was described wherein a pair of counterrotating gyroscopes are used to move a rotary arm of a machine tool. However, the use of two gyroscopes is believed to be unnecessary as a single CMG-type gyroscope should provide sufficient precession torque to move a rotary arm.
Accordingly, it is a broad object of the invention to use a single gyroscope to rotate a member in a single plane with little or no reaction forces being coupled to the support for the rotating member. It is another object of the invention to provide machine tools, such as a swinging arm robot, wherein precession of a single gyroscopic mass is used to provide rotational energy so that little or no reaction forces from such rotation are generated, increasing accuracy and efficiency of machining operations. It is yet another object of the invention to provide a machine tool as described wherein a rotatable member is accelerated and decelerated by precession of a gyroscopic mass, and driven at a constant velocity by a servo mechanism. Other objects and improvements will become apparent upon a reading of the following appended specification.